Is it time for bagworms to hatch out and begin eating?

May 16, 2006

Question Is it time for bagworms to hatch out and begin eating?

Answer First, I need to make sure we are talking about the same critter. Bagworms are caterpillars that make a cocoon shaped like a diamond. They do not make webs which resemble large spider webs. This is the problem with using common names. The word bagworm may be the name a person calls any number of caterpillars. Extension agents refer to this creature by its proper Latin name, Thyridopteryx ephemeraeformis -- yeah right.

Bagworm eggs hatch toward the end of May or first week in June. These cute little worms are only 1/8 of an inch long. Instinctively, they begin to test the strength of their silk by spinning a silk thread and hanging around. Spring breezes catch the wee little worms and blow them to greener pastures. Actually, green pastures for a baby bagworm is a long line of Leyland cypress trees.

If a bagworm is lucky enough to land on a suitable host plant, then it spins a silk cocoon. This cocoon serves as protection from predators, sunlight, pesticides, etc… Foliage from the host plant is cleverly incorporated into the silk cocoon. Bagworms were the original inventors of the ghillie suit.

As the bagworms feed on the foliage of the plant (usually a juniper or arborvitae), they grow and enlarge their silk protection. Homeowners finally begin to spot these pests in August or September. By then, the feeding damage is also very obvious.

Young caterpillars are easy to kill. Mature caterpillars with a protective silk shell are difficult to kill. Therefore, launch the pesticide assault in late May or early June.

Products containing Bt (Bacillus thuringiensis), like DiPel or Worm Whipper, are not contact insecticides. They have to be eaten by the caterpillar. Simply spray the Bt on the foliage and let the bagworms nibble. After a couple bites, they develop a stomach ache that won’t go away. This target specific, non-contact type of pesticide bypasses the protective cocoon and is very safe to the applicator and surrounding environment. However, it does not work very well on mature caterpillars.

Contact insecticides like Sevin, Malathion or Orthene are also more effective when the caterpillars are young. By the end of August or September, bagworms are nearly invincible.

For more information about bagworms visit http://www.ces.ncsu.edu/depts/ent/notes/O&T/trees/ort081e/ort081e.htm

If you don’t have internet access, don't hesitate to call the Extension Office at 893-7533, write us at PO Box 1089, Lillington, NC 27546, or email me at gary_pierce@ncsu.edu

Another name for the ghillie suit is yowie. Ironically, this is also the word most often spoken in September when homeowners realize how many bagworms are eating on their Leyland cypress tree.